1. Field of the Invention
This invention relates generally to electrical pulse signal generators and more particularly to a sub-nanosecond, kilovolt pulse generator for use in impulse radar apparatus, active electromagnetic signal jammers, and relatively high power microwave weapon systems.
2. Description of the Prior Art
Recently there has been much research activity into the generation of nanosecond type pulses utilizing a high power photoconductive solid state semiconductor switch coupled to a storage device. In the above cross referenced related application, there is disclosed a sub-nanosecond pulse generator using a radial transmission line comprised of a photoconductive bulk GaAs switch embedded in a circular dielectric disc of constant thickness with radial type layers of metallization formed on top and bottom surfaces thereof. In one embodiment, the layers of metallization are generally circular in configuration with continuous surface areas. In another embodiment, the continuous surface areas of metallization are replaced by a plurality of outwardly extending stripline segments which converge to a region of common metallization at the middle.
Since the characteristic impedance of such a device is inversely proportional to the width of the dielectric separating the top and bottom layers of metallization, the radial transmission line creates a non-uniform characteristic impedance primarily due to its geometrical configuration. Therefore, at a location outward from the center of the radial transmission line, the impedance is smaller compared to that at a location closer in. When the radial transmission line is charged and the photoconductive switch is optically activated, traveling waves begin to flow from the low impedance region to the high impedance region and in the process,, voltage transformation occurs. The variation of this characteristic impedance between the inner edge and outer edge of the radial transmission line acts like a built in voltage step-up transformer. Accordingly, the degree of impedance variation in the radial line will determine the magnitude of voltage gain at a load connected to the device.
For practical system applications, an optically activated hybrid pulser should produce high peak power pulses with subnanosecond risetime. In addition, the pulser should operate reliably for a long period of time.